Plant and gut microbiota-derived protein metabolites and potential health functions

Bioactive peptides can be obtained from protein hydrolysates through in vitro enzymatic hydrolysis, gastrointestinal digestion, and microbial fermentation. Recent emerging research suggests that prebiotic-stimulated gut microbiota also plays a role in generating bioactive peptides and amino acids in gut. In this study, we examined if enzymatic hydrolysis of soybean and wheat germ, plant materials often used in oil industry, can generate antihypertensive peptides and determined if prebiotic digestive enzymes can induce the production of gut microbiota-derived amino acids. In the first experiment, soybean and wheat germ were hydrolyzed by protease enzymes. Then, their hydrolysates were subjected to peptide isolation and identification. Identified peptides were subjected to test for their potential antihypertensive activities. For the second experiment, rodents were fed an Aspergillus-derived protease- or lipase-mixed diet for 2 weeks. Then, cecum contents were collected for bacteria and metabolite analyses. As a result, we found that His-Gly-Lys from soybean hydrolysate strongly inhibited angiotensin II-induced elevated intracellular Ca2+ concentration in vascular smooth muscle cells (VSMCs). Trp-Val and Trp-Ile from wheat germ hydrolysate were found to inhibit Ca2+-calmodulin (CaM)-dependent protein kinase II (CaMK II), a protein kinase promoting hypertension by inducing Ca2+ influx into VSMCs, in rat thoracic aorta rings. These findings suggest the potential of the plant-derived peptides in preventing hypertension and vascular-related diseases. In the second experiment, we found that the dietary protease and lipase increased Bifidobacterium and Lactobacillus probiotics and induced the production of probiotic-derived amino acids, taurine, ornithine, and γ-aminobutyric acid. Since these amino acids have versatile functions including in gut health modulation and brain functions, it can be hypothesized that the dietary prebiotic-digestive enzymes may be beneficial for gut health and brain functions. This study suggests the possibility of applying oil processing by-products in the production of functional food ingredients including bioactive peptides and amino acids.